Tonight, a stunning upset in a political primary. The House Majority Leader, Eric Cantor, has lost the Republican primary election in Virginia. Cantor was upset by a Tea Party-backed underdog. And for more, I'm joined now by NPR's national political correspondent Mara Liasson. And, Mara, I said this is shocking - I don't think anybody saw this coming.

MARA LIASSON, BYLINE: Nobody saw this coming. This is a complete surprise. It's been called an earthquake. The storyline this year was the Tea Party was vanquished everywhere. But tonight, it's proved that the Tea Party establishment fight is still alive and kicking. This was a devastating upset. Eric Cantor lost by a wide margin. Although there were some internal Virginia state Republican Party politics at play, the issues in this race were Tea Party issues. Eric Cantor was forced to the right on immigration reform. He ran ads against amnesty. Tea Party activists in his district were angry that he voted to end the government shutdown, raise the debt ceiling. And what's even more ironic is that Eric Cantor has courted the Tea Party. He styled himself as a kind of grassroots conservative counterweight to John Boehner, the more moderate speaker. So he did try to straddle the divide and he clearly failed.

BLOCK: So tell us about the Tea Party underdog who vanquished him today. Who is David Brat?

LIASSON: Well, David Brat is an economics professor at Randolph-Macon College. And just to give you an example of how completely improbable his victory was tonight - at the end of March, he reported $40,000 in campaign funds on hand, Eric Cantor had 2 million. And interestingly enough, David Brat will go on to face another professor at Randolph-Macon College - Democrat Jack Trammell - in the fall.

BLOCK: And this is a solidly Republican district, Mara, would the Democrats be looking at this possibly as a pickup now or is that out of the question?

LIASSON: Well, I think anytime you have something like this happen, Democrats will look at possibly as a pickup. But this was considered a pretty safe seat. No one expected Cantor to be defeated. But, you know, there are some other implications for the party. I think this is going to be a real blow to the solar plexus of Republicans who thought that the establishment was reestablishing control over the Tea Party. I think this is going to be a setback for the prospects for immigration reform, and Republicans in the house are going to be very wary of crossing the Tea Party because the message of this primary season up until now was don't worry you won't have to be so afraid of a Tea Party challenge. Well, when Eric Cantor, the guy who was widely considered to be the future speaker of the House, gets defeated in a primary, that's something to really be worried about.

BLOCK: Sure. It's got to set off shockwaves through the rest of the Republican Party and especially vulnerable Republicans who are facing primary challenges of their own across the country.

LIASSON: That's right. We're still waiting to see what happens to Lindsey Graham in South Carolina. He has some Tea Party challengers, the big question not so much is whether he will get the most votes but whether he'll avoid a runoff. And don't forget, in Mississippi we have Thad Cochran, the sitting incumbent Republican Senator who was forced into a runoff by a Tea Party challenger. That runoff is June 24. He is the underdog in that race right now. So I think everybody has to reconsider the conventional wisdom that the Tea Party was shut out this year. They certainly were not.

BLOCK: OK, Mara. Thank you.

LIASSON: Thank you.

BLOCK: That's NPR's Mara Liasson reporting on today's major political upset. Again, House Majority Leader Eric Cantor has lost to his primary election opponent David Brat, who was backed by the Tea Party. Transcript provided by NPR, Copyright NPR.